Electromechanical transducer



Dec. 12, 1967 R. A. GAULT 3,358,088

ELECTRQMECHANICAL TRANSDUCER Filed June 5, 1964 m i /2 k/Z L INVENTORROBERT A. GAULT FIGURE 3. W 9

ATTORNEY United States Patent 3,358,088 ELECTROMECHANICAL TRANSDUCERRobert A. Gault, Paducah, Ky., assignor to CTS Corporation, Elkhart,Ind., a corporation of Indiana Filed June 5, 1964, Ser. No. 373,024 7Claims. (Cl. 179-1155) ABSTRACT OF THE DISCLOSURE An electromechanicaltransducer having a thermally conductive material bonded in closethermal proximity to the winding of the voice coil for increasing therate of heat dissipation from the voice coil during operation. Withincreased dissipation of heat from the voice coil the wattage rating ofthe transducer may be appreciably increased.

The present invention relates to transducers, and, more particularly, toan electromechanical transducer of the type commonly employed in radios,television sets, hig fidelity and stereo sets, and the like.

During the past decade the wattage rating of amplifiers for equipmentsuch as high fidelity and stereo sets has increased considerably.Consequently, it has been necessary to supply electromechanicaltransducers capable of handling the high output wattage of theamplifiers. In most designs, the size of the diaphragm of the transducerremains the same, and only the size of the magnetic structure and thevoice coil associated therewith for operating the diaphragm is increasedto withstand the higher wattage delivered by the amplifier. It would,therefore, be desirable to provide an electromechanical transducer withmeans for increasing the wattage rating without increasing the size ofthe magnetic structure or thevoice coil.

Generally one of the wattage rating limitations of an electromechanicaltransducer is the thermal dissipation of the voice coil and theassembly. By improving the dissipation factor of the voice coil, thetransducer not only can be rated at a higher wattage but the transducercan also be subjected to a higher current overload. Generally,

the damage to an electromechanical transducer from a current overload isthe result of the voice coil being unable to dissipate the excessiveheat generated by the increased wattage carried by the coil. It has beensuggested to make the bobbin of the voice coil of a metallic materialhaving a sufiicient thickness so as to be self-supporting. Considerabledifliculty has been experienced, however, in adhesion of the turns ofthe magnet wire forming the winding of the voice coil to the metallicmaterial. Further, the possibility of shorting of the turns forming thewinding is also increased when the winding is bonded directly to themetallic material. In the past, various experiments have also revealedthat the heat may be dissipated more rapidly by attaching fins or othersuitable heat dissipating means to the voice coil. Such heat dissipatingmeans have, however, been virtually ineffective inasmuch as they alsosubstantially increase the mass of the voice coil. Moreover, theincreased mass increases the inertia of the diaphragm attached to thevoice coil, the increase in inertia being especial-1y detrimental athigher frequencies thereby decreasing the efliciency of the transducer.

In some electromechanical transducers, such as loudspeakers, theefliciency of the loudspeaker at high frequency response has beensomewhat improved by mounting a ring of aluminum in spaced relationshipto the voice coil. The attachment of the ring to the voice coil iseffected through a resilient coupling, e.g., rubber bands. Thus, at highfrequencies, the voice coil has little effect in causing the diaphragmto vibrate, and the diaphragm "ice is vibrated primarily by the ring ofaluminum which receives the high frequency current by induction from theenergized winding of the voice coil. Further details of a similarconstruction are shown in Barker Patent No. 2,164,374, dated July 4,1939. Although such loudspeaker designs are eflicient at both the highand low frequencies, the wattage rating of the voice coil is stilllimited especially at low frequencies inasmuch as the heat generated inthe voice coil is not rapidly dissipated by the ring of aluminumresiliently secured by the thermally nonconducting means to the voicecoil. It would, therefore, be desirable to provide a loudspeaker with avoice coil having a thermally conductive means in close proximity to thevoice coil for rapidly dissipating the heat generated by the voice coil.

Accordingly, it is an object of the present invention to provide animproved electromechanical transducer having the desirable features setforth above.

Another object of the present invention is to provide anelectromechanical transducer with a voice coil having a thermallyconductive foil bonded in close thermal proximity therewith.

A further object of the present invention is to provide anelectromechanical transducer with a bobbin of laminated material, one ofthe laminations of the bobbin being of electrically nonconductivematerial for supporting and insulating the turns of the magnet wireforming the winding of the voice coil and the other lamination being ofa thermally conductive material for rapidly dissipating the heatgenerated by the voice coil thereby increasing the wattage rating of thetransducer.

Still another object of the present invention is to provide anelectromechanical transducer with a cylindrical voice coil having abobbin disposed in the air gap of the magnetic structure with turns ofmagnet wire forming a winding on one side of a bobbin and an aluminumfoil on the other side of the bobbin bonded to the bobbin for rapidlydissipating the heat generated by the voice coil when subjected to asustained current overload.

Further objects and advantages of the present invention will becomeapparent as the following description proceeds, and the features ofnovelty characterizing the invention will be pointed out withparticularity in the claims annexed to and forming a part of thisspecification.

Briefly, the present invention is concerned with an electromechanicaltransducer, e.g., a loudspeaker, having a thermally conductive materialbonded and in close thermal proximity to the winding of the voice coilfor increasing the heat dissipation of the voice coil in order that thewattage rating of the transducer may be increased.

For a better understanding of the present invention, reference may behad to the accompanying drawings wherein the same reference numeralshave been applied to like parts and wherein:

FIGURE 1 is a sectional view of an electromechanical transducer built inaccord with the present invention;

FIGURE 2 is an enlarged fragmentary section of FIG- URE 1 showing thevoice coil and pole structure; and

FIGURE 3 is a sectional view taken along line III-III of FIGURE 1,assuming that FIGURE 1 is shown in full.

Referring now to the drawings, there is illustrated an electromechanicaltransducer, e.g., a loudspeaker, generally designated at 10, comprisinga dish-like supporting frame 11 having secured thereto a stationarymagnetic structure 20.

Considering first the stationary magnetic structure 20, it comprises apermanent magnet 21, a yoke 22, and pole pieces 23 and 24 securedtogether by welding or the like. The stationary magnetic structure 20 isfixedly secured to the base portion 12 of the supporting frame 11 bysuitable means such as screws. The stationary magnetic structure 20 hasan E cross-section as shown in FIGURE 1 of the drawings. The yoke 22 andthe pole pieces 23 and 24 are preferably of iron or other suitable softmagnetizable material. As best seen in FIGURE 3 of the drawings, thepole pieces 23 and 24 actually are one pole as shown in FIGURE 3 and theother pole 26 encircled by the pole pieces 23 and 24 defines an annularair gap for the stationary magnetic structure.

For the purpose of transforming electrical energy into acousticalenergy, the transducer 1% is provided with a diaphragm 3t) and a voicecoil 4t), the outer edge 31 of the diaphragm 3%) being corrugated so asto offer slight resistance to movement of the diaphragm in the axialdirection but to provide sufiicient resistance to transverse movement ofthe diaphragm. The outermost peripheral edge 32 of the diaphragm isfixedly secured with a suitable adhesive to the outer edge 13 of thesupporting frame 11. It is to be understood, however, that the outeredge 31 of the diaphragm need not be corrugated and fixedly secured tothe frame 11. One end of the voice coil 40 is fixedly secured to theapex 33 of the diaphragm and the other end of the voice coil is disposedin the air gap 25. Generally, proper suspension of the voice coil 46 inthe air gap is maintained by a spider 34 extending outwardly of thevoice coil and having its inner edge fixedly secured thereto, the outeredge of the spider 34 being fixedly secured to the supporting frame. Thespider 34 is preferably of a suitably impregnated cloth or paper formedwith annular corrugations to provide a high degree of flexibility in anaxial direction and substantial stiifness in the radial directiontransverse thereto. A dome shaped dust cover 35 is adhesively secured tothe inner cone portion of the diaphragm for maintaining the voice coil49 and the air gap 25 free of foreign particles.

In order to vibrate or move the diaphragm 30 and the voice coil 49 inresponse to changes in electrical energy, e.g., by changing the current,the voice coil comprises a winding 41 of magnet wire having a pair ofnot-shown leads connected to the output of an amplifier. Thus a changingcurrent in the winding 41 associated with a magnetic field in the airgap 25 functions in such a manner so as to force the voice coil axiallyof the air gap 25 causing the diaphragm 3i) attached to the voice coil40 through the apex 33 to develop acoustical energy.

Considering specifically the voice coil 40, it comprises a bobbin 42preferably of an electrically insulating material such as paper orplastic, supporting the winding 41. In accord the present invention, athermlly conductive material 43, e.g., an aluminum foil, or a materialhaving a high density of metal particles, is adhesively secured orbonded preferably to the entire inner surface of the bobbin 42. It is tobe understood, however, that the thermally conductive material 43 couldbe adhesively secured to only a portion of the inner surface or to theouter surface of the bobbin provided that sufficient insulating means isprovided to prevent the magnet Wire from shorting the adjacent turns ofthe winding 41. Inasmuch as most thermally conductive materials such asaluminum foil have sufiicient structural strength, it is possible toreduce the thickness of the material forming the bobbin to maintain thetotal mass at a minimum and not effect the combined inertia of thediaphragm 30 and the voice coil 49. Moreover, the thermally conductivematerial improves the dimensional stability of the bobbin since suchmaterials do not absorb moisture and the like.

The thickness of the aluminum foil 43 and the material forming thebobbin vary depending upon the size of the transducer. For example, in adevice built in accord with the present invention, the total thicknessof the aluminum foil 43 and the paper of a bobbin of an eight inchloudspeaker was .006 inch, the aluminum foil preferably being muchthinner than the electrically insulating material and approximately .801inch in thickness. Other thermally conductive materials such as copperfoil may also be used but aluminum is preferable due to its lightness.Magnetically conductive materials should not be employed for thermallyconductive materials since they would affect the performance of thevoice coil in the air gap. It has been found that best results areobtained by laminating the thermally conductive material to the paper ina suitable manner before the bobbin is formed into a tube or the like.Satisfactory results have, however, been obtained by bonding an aluminumfoil to a formed bobbin.

From the above description, it will be apparent that the same sizetransducer employing the improved voice coil of the present inventioncan be rated at a higher wattage since any heat generated by the voicecoil is rapidly dissipated by the thermally conductive material 43,e.g., the aluminum foil, forming a part of the bobbin carrying the voicecoil.

The present invention will readily be understood in view of the detaileddescription included above, and no further discussion regarding theoperation of the electromechanical transducer is included herewith. Itwill be appreciated that the voice coil of the transducer of the presentinvention can also be subjected to a substantially greater currentoverload than heretofore without damaging the voice coil to any extentbecause the heat generated by the overload current is rapidly dissipatedthrough the aluminum foil.

While there has been illustrated and described what is at presentconsidered to be a preferred embodiment of the present invention, itwill be appreciated that numerous changes and modifications are likelyto occur to those skilled in the art, and it is intended in the appendedclaims to cover all those changes and modifications which fall withinthe true spirit and scope of the present invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. In an electromechanical transducer; the combination of a supportingmeans; a magnetic structure carried by the supporting means; a voicecoil operably associated with the magnetic structure, the voice coilcomprising a bobbin of electrically insulating material having apredetermined thickness, a winding disposed on the outer surface of thebobbin, and a lamination of thermally conductive material fixedly bondedto the inner surface of the bobbin adjacent to the winding fordissipating the heat generated by the winding, said lamination ofthermally conductive material having a thickness less than saidpredetermined thickness; and means operably connected to the voice coilfor developing acoustical energy upon energization of the winding of thevoice coil.

2. An electromechanical transducer comprising a dishlike supportingframe, a stationary magnetic structure fixedly secured to the framehaving a generally E shaped cross-section and including a magnetprojecting a field between the inner arm of the E serving as one poleand the outer arms serving as the other pole, a diaphragm having an apexand a corrugated outer edge secured to the frame, a cylindricallaminated bobbin circumposing the one pole and attached to the apex ofthe diaphragm, one lamination of the bobbin being of a thermallyconductive material and the other lamination of the bobbin being of anelectrically insulating material, said thermally conductive materialhaving a thickness less than the thickness of said electricallyinsulating material, and a winding carried by the laminated bobbin forcarrying a changing current associated with a changing magnetic field,the magnetic field cooperating with movement of the bobbin attached tothe diaphragm through the apex.

3. In an electromechanical transducer the combination of a supportingframe, a stationary magnetic structure fixedly secured to the frame andhaving an E shaped crosssection including a magnet projecting a fieldbetween the inner arm of the E serving as one pole and the outer armsserving as the other pole to define an air gap therebetween, a diaphragmhaving an apex and a corrugated outer edge fixedly secured to thesupporting frame, a bobbin of electrically nonconductive materialdisposed in the air gap and secured to the apex of the diaphragm, awinding of magnet wire attached to one side of the electricallynonconductive bobbin for carrying a changing current associated with amagnetic field of the magnetic structure, and a thermally conductivematerial fixedly attached to the other side of the bobbin and in closeproximity with the winding for providing a continuous and uninterruptedpath for conducting heat away from said voice coil thereby to rapidlydissipate the heat generated by the winding during operation, saidthermally conductive material having a thickness less than the thicknessof the electrically insulating material and the magnetic fieldcooperating with movement of the bobbin attached to the diaphragmthrough the apex.

4. In an electromechanical transducer, the combination of a supportingframe, a stationary magnetic structure fixedly secured to the supportingframe, a bobbin disposed in the air gap of the stationary magneticstructure, a diaphragm having an apex fixedly secured to the bobbin, awinding attached to one side of the bobbin for carrying a changingcurrent associated with a magnetic field of the stationary magneticstructure, said bobbin consisting of an electrically nonconductivematerial, and a thermally conductive material fixedly bonded thereto inclose proximity to the winding whereby upon energizing the winding theheat generated by the winding is rapidly dissipated by the thermallyconductive material.

5. In an electromechanical transducer having a stationary magneticstructure, a voice coil operably associated with the stationary magneticstructure, said voice coil comprising a winding for energization duringoperation, and a diaphragm secured to the voice coil the improvement insaid transducer comprising, a bobbin for supporting the winding, saidbobbin consisting of a first lamination of thermally conductive materialand a lamination of electrically nonconductive material fixedly bondedto said first lamination, said winding Wound on said bobbin in closeproximity to said first lamination whereby during operation the heatgenerated by the winding is rapidly dissipated by the first lamination.

6. The electromechanical transducer of claim 5, wherein the laminationof thermally conductive material is substantially thinner than thethickness of the lamination of electrically non-conductive material andsaid nonconductive material is paper.

7. The electromechanical transducer of claim 5, wherein the laminationof thermally conductive material is substantially thinner than thethickness of the lamination of electrically nonconductive material andsaid nonconductive material is plastic.

References Cited UNITED STATES PATENTS 2,485,745 10/1949 Koonz 336-612,769,942 11/1956 Hassan 179115.5 3,160,716 12/1964 Luth 179115.5

KATHLEEN H. CLAFFY, Primary Examiner.

A. A. MCGILL, Assistant Examiner.

5. IN AN ELECTROMECHANICAL TRANSDUCER HAVING A STATIONARY MAGNETICSTRUCTURE, A VOICE COIL OPERABLY ASSOCIATED WITH THE STATIONARY MAGNETICSTRUCTURE, SAID VOICE COIL COMPRISING A WINDING FOR ENERGIZATION DURINGOPERATION, AND A DIAPHRAGM SECURED TO THE VOICE COIL THE IMPROVEMENT INSAID TRANSDUCER COMPRISING, A BOBBIN FOR SUPPORTING THE WINDING, SAIDBOBBIN CONSISTING OF A FIRST LAMINATION OF THERMALLY CONDUCTIVE MATERIALAND A LAMINATION OF ELECTRICALLY NONCONDUCTIVE MATERIAL FIXEDLY BONDEDTO SAID FIRST LAMINATION, SAID WINDING WOUND ON SAID BOBBIN IN CLOSEPROXIMITY TO SAID FIRST LAMINATION WHEREBY DURING OPERATION THE HEATGENERATED BY THE WINDING IS RAPIDLY DISSIPATED BY THE FIRT LAMINATION.